Amorphous silicon, copper indium gallium diselenide (CIGS), and cadmium telluride (CdTe) are the only thin film solar cells that are being produced in commercial scale today. Thin film solar cells on flexible substrates that are currently available include amorphous silicon on a thin metal foil (usually stainless steel) and CIGS on metallic or polyimide foils. To date, thin film cadmium telluride solar cells are produced only on glass, but work is being done on a flexible substrate. Other types of solar cell materials suitable for use on flexible substrates may become available. For example work is being carried out on a variant of CIGS that utilizes zinc and tin instead of indium and gallium, as well as continuing research on organic and dye sensitized solar cell materials.